Medicago polymorpha L., california burclover. Annual, taprooted, several–stemmed at base, forming lateral branches along along principal axes, prostrate and mat–forming to decumbent, 10—40 cm tall; shoots glabrate to inconspicuously short–strigose aging glabrescent; roots nodulated.
Stems 4–ridged, to 3 mm diameter, with 3 ridges descending from each leaf, green to purple–red, tough or not, internodes to 70 mm long, outer 2 faces concave, other faces convex on upper internode becoming flat on lower internode; on robust shoots hollow.
Leaves alternate distichous to helically alternate, pinnately 3–foliolate with paired lateral leaflets, petiolate with pulvinus, with stipules; stipules 2, fused along petiole base below pulvinus and persistent, semi–ovate in outline, 3.5—12.5 × 2—5.5 mm, lobed at base, jagged on margins with 9—23 teeth, the teeth 1–veined and acuminate to linear, (0.3—)1—3(—4.5) mm long, fading to pale green where fused to petiole, glabrous; petiole shallowly channeled above pulvinus, 13—35 mm long, glabrous or sparsely strigose, typically with a few hairs at junction with rachis; rachis shallowly channeled, 0.8—7 mm long, glabrous but with a few hairs at junction with petiolules, sometimes with a few, scattered, fine straight hairs; petiolules = pulvinus, 0.5—1.2 mm long, pinkish to pale green; blades of leaflets obovate to ovate, rhombic, or heart–shaped, 5—24 × 5.3—19 mm, terminal leaflet > lateral leaflets, tapered at base, short–toothed on margins mostly above midblade, notched at tip with short point, the point reddish and inconspicuously pubescent, pinnately veined with parallel and evenly spaced lateral veins and midrib raised on lower surface, each vein extending as a minute point on the margin, upper surface glabrous, lower surface sparsely strigose at least along midrib or becoming glabrescent.
Inflorescence raceme, somewhat headlike with flowers crowded at top, axillary, in range to 22–flowered often with 2—5 flowers per node, bracteate; peduncle slender, at anthesis ascending and 2—17 mm long increasing 2× and spreading to ascending in fruit, short–strigose; bractlet subtending pedicel awl–shaped, 1—1.5 mm long; pedicel 0.3—0.6 mm long.
Flower bisexual, bilateral, pealike (papilionaceous), 3—3.5 mm across; nectary nectar–producing receptacle below ovary; calyx 5–lobed, 2.5—3.7 mm long, short–strigose; tube bell–shaped, faintly 10–veined, sometimes purple–spotted at sinuses; lobes = tube length, subequal, long–acuminate, with conspicuous midvein; petals 5, bright yellow; banner slightly clawed or lacking claw, spreading and arching upward, obovate, 3.5—5 × 3.1—3.7 mm, tapered at base, notched at tip, with ca. 6 purplish to dark red, radiating nectar lines; wings 2, clawed, 3.3—3.7 × 1.1—1.4, < banner, lobed at base, whitish on claw and lobe; keel of 2 petals partially fused on lower edge of limbs, clawed, 3—3.2 × 0.8—1.1 mm, wings > keel, claw ca. 1.5 mm long, lobed at limb base, whitish on lobe and claw; stamens 10, diadelphous (9 filaments fused and 1 free); filaments sheet 2—2.5 mm long, filament free portions < 0.5 mm long, free filament 1.6—2 mm long, pale green; anthers basifixed, dithecal, < 0.2 mm long, yellowish, longitudinally dehiscent; pollen yellowish; pistil 1; ovary superior, compressed crescent–shaped to linear and partially twisted, 2 mm long, ± cobblestonelike, 1–chambered with several ovules attached to upper side; style upturned; stigma narrowly umbrellalike (peltate), green, densely fringed from below with kinky hairs.
Fruit pod (legume), indehiscent, 4—6–seeded, 2—6–coiled, 4.5—8 × 7—10 mm, with 2 rows of prickles on outer margin, the prickles minutely hooked and spreading, 1—2 mm long.
Seed kidney–shaped, 2.5—3.2 × 1.5—1.9 mm, light tan.
A. C. Gibson & B. A. Prigge